This invention relates to a process for the generation of transmission current signals in an alternating current distribution network by means of a transmitter connected to the network and equipped with a controlled switch. In this process, a series of current impulses forming the transmission signal is produced by operation of the switch and the points in time at which these impulses are produced and/or their duration are so chosen that the resulting transmission signal corresponds at least approximately to a desired theoretical signal.
A process of this kind described in European Patent Application No. 85 108 615.7 (Publication Number 0 175 863) corresponding to U.S. Pat. No. 4,642,637, has the advantage that it dispenses with the frequency selective coupling circuits required in other known processes and replaces them by a substantially aperiodic network. This enables the same transmitter to be used for different transmission frequencies and enables redundancy to be introduced into the transmission channel since the signals can be transmitted at different frequencies. The reliability of transmission is thereby considerably enhanced.
The above-mentioned network may in principle be composed either of reactive components or of ohmic components but more detailed analysis shows that, firstly, no choke coil may be directly connected in series with the switch unless the latter is designed for a very high return voltage and, secondly, no capacitor may be directly connected to the switch, i.e., connected to the supply voltage or another capacitor through the switch, unless the switch is designed for very high peak currents which would, however, entail a considerable increase in cost.
If, on this basis, the use of series chokes and parallel capacitors is prohibited, at least in the absence of powerfully damping ohmic components, then such a network has little advantage over a simple resistor. A resistor, however, would have the disadvantage of consuming a considerable supply frequency power. The disadvantage of this lies not so much in the high cost of the energy consumption but rather in the amount of heat which is generated and has to be removed.